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Viruses 2018, 10(1), 25;

Geometric Defects and Icosahedral Viruses

Indiana University Electron Microscopy Center, Indiana University, Bloomington, IN 47405, USA
Department of Biology, Indiana University, Bloomington, IN 47405, USA
Molecular and Cellular Biochemistry Department, Indiana University, Bloomington, IN 47405, USA
Authors to whom correspondence should be addressed.
Received: 20 November 2017 / Revised: 26 December 2017 / Accepted: 28 December 2017 / Published: 4 January 2018
(This article belongs to the Special Issue Advances in Structural Virology via Cryo-EM)
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We propose that viruses with geometric defects are not necessarily flawed viruses. A geometric defect may be a reactive site. Defects may facilitate assembly, dissociation, or accessibility of cellular proteins to virion components. In single molecule studies of hepadnavirus assembly, defects and overgrowth are common features. Icosahedral alphaviruses and flaviviruses, among others, have capsids with geometric defects. Similarly, immature retroviruses, which are non-icosahedral, have numerous “errors”. In many viruses, asymmetric exposure of interior features allows for regulated genome release or supports intracellular trafficking. In these viruses, the defects likely serve a biological function. Commonly used approaches for spherical virus structure determination use symmetry averaging, which obscures defects. We suggest that there are three classes of asymmetry: regular asymmetry as might be found in a tailed phage, irregular asymmetry as found, for example, in defects randomly trapped during assembly, and dynamic asymmetry due to Brownian dynamics of virus capsids. Awareness of their presence and recent advances in electron microscopy will allow unprecedented investigation of capsid irregularities to investigate their biological relevance. View Full-Text
Keywords: capsid; nucleocapsid; hepadnavirus; alphavirus; self-assembly; cryo-electron microscopy capsid; nucleocapsid; hepadnavirus; alphavirus; self-assembly; cryo-electron microscopy

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Wang, J.C.-Y.; Mukhopadhyay, S.; Zlotnick, A. Geometric Defects and Icosahedral Viruses. Viruses 2018, 10, 25.

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